The present invention relates to a method and a sensor for the measurement of temperature, and more specifically, to a method and a sensor for the measurement of absolute temperature in which calibration of the sensor is not required prior to the measurement of temperature.
Essentially all physical, chemical, and biological processes depend to some extent on temperature. Devices that employ such temperature-dependent processes often have a range of absolute temperature that is conducive to proper device operation as well as one or more ranges of absolute temperature where proper device operation can foreseeably be ruled out. In some cases, the latter temperature range moreover induces irreversible modifications of general device functionality, such that these temperatures should be avoided. To ensure proper functional operation of the device, it is therefore often desirable to monitor the absolute temperature of the device during device operation and control the temperature and/or device operation such that the potential for any harm to the device due to device operation at improper temperatures is reduced or even eliminated.
This holds true, for example, during the operation of semiconductor devices and, more specifically, for the operation of integrated circuits (“ICs”). For ICs, it can, for example, be desirable to operate the IC at an absolute temperature higher than, e.g., 250K and lower than, e.g., 360K. To ensure IC device operation in this (or some other) desirable temperature range, the absolute temperature of the IC should be measured at least periodically during device operation (e.g., once every second) and utilized in a control type process and/or system that prevents IC device operation in an undesirable temperature range and/or provides some type of corrective action to allow for device operation in a desirable temperature range.
Determining a temperature difference of a device at any particular instance in time during device operation is generally easier than determining the absolute temperature of that device. Consider for instance a resistive temperature sensor, where the temperature-dependent change of a specific resistivity of a material (e.g., platinum) is used to infer the temperature. If the resistance at a first temperature is known, then from a measurement of the resistance at a second temperature the temperature difference between the first and second temperatures can be accurately determined. Yet, using a resistive temperature sensor to measure the absolute temperature of a device inherently necessitates first determining the resistance of the temperature sensor at a known first temperature, i.e., it is typically necessary to calibrate the temperature sensor prior to using it to measure the actual temperature of something.
For devices, e.g., semiconductor integrated circuits, which are typically produced in relatively large numbers, it is impractical from a production efficiency point of view to separately calibrate the temperature sensors attached to or made a part of each one of the separate semiconductor integrated circuits. It is therefore desirable to equip the integrated circuit with a temperature sensor that does not require calibration.
Using a resistance temperature sensor for calibration-free temperature measurement requires that the element (e.g., a platinum strip or a semiconductor diode) which exhibits the temperature-dependent resistance be fabricated such that the resistance variations between different sensors are sufficiently small. Consider for instance a resistance temperature sensor employing a platinum metal strip. At 0° C. the resistance of platinum changes about 0.4% per Kelvin. A calibration-free temperature sensor for determining the absolute temperature to an accuracy of ±5K therefore requires that resistance is known with an accuracy of about ±2%. Fabricating such sensors with resistances varying by less than ±2% from sensor to sensor is challenging; in particular, because the resistance depends on the sensor dimensions (e.g., the platinum film thickness). Thus, it is most often not practical to utilize a resistance temperature sensor for calibration-free temperature measurement, especially in conjunction with temperature measurement of integrated circuits.